PROJECT SUMMARY Barrett?s esophagus (BE) is the only known pre-cancer lesion of esophageal adenocarcinoma (EAC) which has seen a 600% increase in incidence. However, the cellular and molecular mechanism driving BE initiation and progression remains undetermined, and the knowledge gap prevents us from identifying meaningful therapeutic targets for the treatment of the pathological entity. This application will build on our recent findings that the novel transitional basal stem cells contribute to Barrett?s metaplasia in both mouse genetics and human organoid models. We will study the molecular mechanism promoting the intestinal differentiation of the unique stem cell population. Our preliminary data suggest that Wnt signaling and its downstream target SOX4 play critical roles in the pathogenesis of BE. Therefore we will test the hypothesis that the Wnt/SOX4 axis promotes Barrett?s metaplasia and that pharmacological inhibition of the axis blocks BE progression. We have designed three aims to test this hypothesis: (1) To test the hypothesis that increased Wnt signaling upon chronic inflammation promotes Barrett?s metaplasia of transitional basal stem cells. (2) To test the hypothesis that SOX4 mediates Wnt signaling to promote Barrett?s metaplasia, and (3) To intervene in the Wnt/SOX4 axis for therapeutic gain against BE and EAC. We will use multiple mouse models (e.g. Wnt and SOX4 gain- and loss-of-function) combined with organoid and in vitro assays to address these aims and test candidate drugs identified through an unbiased screen. This work will provide novel insights into the cellular and molecular mechanisms underlying the initiation and progression of BE, and the signaling program we identified will enable discovery of new therapeutic targets.